Expansion joint



J. COOPER EXPANSION JOINT Jan. 23, 1968 4 Sheets-Sheet 1 Filed April 4, 1966 INVENTOR.

' JACOB COOPER I BY A T TOR/VE Y Jan. 23, 1968 J. COOP-ER 3,365,217

EXPANSION JOINT Filed April 4, 1966 4 Sheets-Sheet 2 T 'F/d/ "War I (I "I, III NIH |l I 25 I 71 a i I l l] \I I, mi l I 1 2 FM pf \-\/,O

/ r q d INVENTOR.

JACOB COOPER W Q M 5 7 ATTORNEY J. COOPER EXPANSION JOINT Jan. 23, 1968 4 Sheets-Sheet 5 Filed April 1966 INVENTIOR.

JACOB COOPER BY C\ mu -H M111 1% A TTORNE Y Jan. 23, 1968 J. COOPER EXPANSION JOINT 4 Sheets-Sheet 4 Filed April 4, 1966 m w B M Y B w M I w w w. 8 9 6 8 3 w H ATTORNEY United States Patent Ofitice 3351M? Patented Jan. 23, 15568 3,365,217 EXPANSiGN JDENT Jacob Cooper, Livingston, N .J., assignor to Foster Wheeler Corporation, Livingston, Ni, a corporation of New York Filed Apr. 4, i966, Ser. No. 539,937 16 Gaims. (Cl. 235-229) This invention relates to expansion joints, and more particularly, to single fold metallic expansion joints having resilient expansible and contractible corner sections.

Existing metallic expansion joints for boiler lines and ducts of the bellows type provide sufficient flexibility as a result of the accordion-like movement of longitudinal, multiple V-shaped bellows folds. However, to achieve a sufllcient degree of resiliency the metal must be thin and the folds numerous, and generally, sharp. Failures are frequent, and fly ash and combustion products tend to collect and compact in the several folds, decreasing flexibility and causing corrosion, oxidation and breaks in the thin metal. Failures are difficult to repair in the field without replacement of whole sections of the joint since the sharp folds do not permit sufficient room for Weld repair; and with the thin metal, Weld repairs tend to burn through the wall of the joint.

Single fold U-shaped, gas tight flexible joints have been proposed for lines and ducts. However, these joints have not proven entirely satisfactory, especially for large rectangular joints where the stresses in the corners tend to be excessively severe. In an effort to minimize corner stresses in single fold joints, the corner sections have been made wide relative the rest of the joint to permit the corners to buckle or flex to absorb the high tension stresses therein. The corner sections have also been made from metals having a lower modulus of elasticity, or of a thinner gage than the rest of the joint, to provide increased flexibility for the corners. Some corner sections have been made rounded, and certain joints have been made with a rounded U-shape bow fold providing joint and duct flexibility but somewhat restricting flexibility to within limits so that the corner stresses are not excessive. To insure further protection against severe corner stresses, other means were provided to limit the expansive movement of the joint which somewhat defeated the basic purpose intended for the joint. In addition, transverse em bossed grooves have been prewrinkied into corners in an attempt to increase the sidewise corner flexibility. The embossed grooves were curved about the rounded portion of the U-shaped bow fold causing difficulty of manufacture (requiring bending or curving of the fold after the grooves were impressed on flat metal) resulting in weakness in the metal. Moreover, the grooves did not provide for the basic dithculty of the corner sections, namely, the ability to withstand the excessive radial and transverse tensile stresses.

Nothwithstanding these attempts to satisfactorily adapt single fold joints for the purpose intended, these joints still are relatively inflexible, causing the corner sections to become rigid with the build-up of intense radial and transverse tensile forces which restrain the desired expansion movements of the joint and ducts and tend to cause corner section failure, or failure at the Welds where the corner sections are joined to the rest of the joint.

Accordingly, it is an object of this invention to provide an improved single fold expansion joint.

It is an object of this invention to provide a single fold flue and duct expansion joint which greatly reduces, or eliminates, leakage and maintenance and can absorb the corner stresses, without inhibiting movements of the flues and ducts, over an economically useful lifetime.

It is another object of this invention to provide a single fold expansion joint which is inexpensive, readily fabricated and easy to install and repair.

It is another object of this invention to provide a single fold expansion joint having flexure stress characteristics and cost economies superior to prior single fold joints.

It is still another object of this invention to provide a metallic single fold rectangular expansion joint with corner sections uniquely adapted for satisfactory performance.

Therefore, the present invention provides an expansion joint axially connected between passageways consisting of a single, metallic fold. The edges of the corners of the joint are rounded and the corner legs of the fold are cor rugated into a series of radially displaced corrugations conforming to the rounded corner edges. No corrugations are on the corner sections between the legs of the fold. The corrugations transform the radial and transverse tension tending to build up in the corner during longitudinal movements of the passageways, and consequent opening or closing of the fold, into contracting of the corrugations. The corrugations also increase the rigidity of the corners in the circumferential or sidewise direction maintaining the legs of the fold planar about the entire joint.

The corner stress problem is consequently eliminated. The corner corrugations resolve tensile corner stresses into radial flexing of the corrugations enabling the single fold joint to avoid the consequences of otherwise severe corner stresses, rigidity and joint failures. Bending of the corners is transferred into useful expansion. Tension is not developed in the corner sections as the corrugations are designed not to achieve full expansion or contraction for the expected movements of the ducts and joint.

The joint may be made in alternating corner and straight sections welded together; the straight sections are not corrugated and comprise a single piece of metal formed into the fold simply by bending. The corner corrugations providing circumferential rigidity cause the legs of the joint, including the corner section legs and the straight section legs, to act as a planar member thereby minimizing weld failure between sections. The ends of the corrugations terminate in spaced relationship from the squared ends of the corner sections which are welded to the straight section ends providing ease of manufacture and assembly and insuring the integrity of the welds and corrugations.

The corrugations may be conveniently formed explosively, with or without dies. The corrugations can be calibrated to yield the same expansion movements as the non-corrugated straight sections of the joint and are easily balanced from a stress condition providing equal stresses over the joint. The corner of the joint is not downrated, and the sides understressed, to protect against corner failure as was the case with the earlier joints. The metal walls of the joint may be made relatively thin without overall loss of strength. Installation and maintenance can be effected with ordinary stick electrode welding. The corrugations permit the joint to be made smaller at the corners than prior joints providing a savings in cost and space. Improved resiliency of the joint is achieved which permits the joint to perform ideally without restricting thermal movements of the ducts and without establishing objectionable stresses. The corrugations provide adaptable radial and transverse flexibility making this joint also attractive for toggle movement applications where the fold may be under less contraction on one side of the joint than on the other side. The joint is gas-tight and is capable of withstanding high temperatures in pressurized fiues during the entire service life of the equipment. Erosion and corrosion are minimized with the single fold and the joint may be fabricated from noncorrosive materials.

The invention, the above and other objects and advantages will be more fully understood from the following description when considered in connection with the accompanying drawings in which:

FIGURE 1 is a plan view of an expansion joint according to the invention;

FIGURE 2 is a view in elevation of the expansion joint taken along the line 2-2 of FIG. 1;

FIGURE 3 is an enlarged cross-sectional view of the straight section of the joint taken on the line 33 of FIG. 1;

FIGURE 4 is an enlarged view in section of the corner section of the expansion joint taken on the line 4-4 of FIG. 1;

FIGURE 4A is a view in section of a variant corner section arrangement of the joint;

FIGURE 5 is a plan view of the corner section of the expansion joint taken on the line 55 of FIG. 4;

FIGURE 6 is an isometric view of a corner of the expansion joint;

FIGURES 7 and 8 are diagrammatic views of the expansion and contraction conditions of the joint, respectively;

FIGURE 9 illustrates a toggling application of the expansion joint;

FIGURES 10 and 11 show the joint in inverted positions;

FIGURE 11A shows a polygon shaped joint; and

FIGURE 12 is a view in elevation of the joint with an ash cover plate.

Referring to the drawings and more particularly to FIGS. 1 and 2 showing a rectangular expansion joint 15 in accordance with the invention. The joint connects two rectangular ducts or passageways 17 and 19 providing for thermal expansion or contraction of the passageways. The passageways and/or joint may be circular although not shown herein. Links 21 welded to the ends of the passageways and to flanged ends 23 of the expansion joint connect the joint to the passageways in gas-tight relationship.

The expansion joint is constructed from corner sections 25 and straight sections 27 welded together in alternating relationship along squared or right angle ends 29. Each straight section 27, comprising a single metallic piece, is bent into two leg portions 31 (FIGS. 2 and 3) and an intermediate portion 33 forming a squared U-shaped fold without welds therebetween. Similarly, as shown in FIG. 4, the corner sections 25, although elongated, and welded, are formed into a squared U-shaped fold comprising corner leg portions 35 and corner intermediate portion 37 welded together at welds 39. The flanged ends of the corner section, 23, are welded together at 41 and also elongated. The corner section 25, as shown in FIG. 1, somewhat restricts the cross-sectional fiow area of the rectangular passageways since the inner edge 43 is curved; where the flow becomes too restrictive, the duct may be enlarged adjacent the expansion joint similar to the arrangement shown in FIG. 11.

The legs 35 of the corner section are formed with a plurality of corrugations 49 substantially comprising sinusoidal crests 51 and troughs 53, corresponding crests and troughs on both legs 35 being adjacent and in plane symmetry so that the space 55 between the legs defines a region of varying distance therebetween. This symmetry, combined with the other features of the joint, is advantageous to the operation of the joint. For toggling applications (FIG. 9) where one side of the joint, or one leg, is under more compression than the other, the corresponding crests and troughs of the facing legs may be displaced with respect to each other as illustrated in FIG. 4A. However, for toggle applications, as for other applications, the exact disposition of the corresponding crests and troughs of the facing legs in each case is determined to provide optimum reduction of the corner stresses and to provide uniformity of stress over both legs.

The corrugations as are formed into a series of radially displaced concentric arcs as shown in FIG. 5 showing a plan view of a corner leg 35. The radius of each corrugation is drawn from a point t) (FIGS. 1 and 5 The inner edge 43 of the corner also forms an arc concentric to the corrugations with radius from 0, subtending an angle of about The outer edge forms an arc at 57 which preferably subtends a 90 angle but has a smaller radius than the radius of the inner edge and an origin 0' closer to the outer edge than ti, permitting the tangent ends 5? of the outer edge are 57 to match the straight outer edge 61 of the straight sections 27 (FIG. 1 upper right-hand corner), minimizing the stress at the welded ends 2). All corrugations and curved corner edges (arcs 43 and 57) are symmetrical about the 45 angle line R.

The corrugations closest to the inner edge 43 are longest subtending an arc of 90, the corrugations gradually decreasing in angle subtended for the corrugations 63, 64 and s5, respectively, approaching the outer edge. The are of the outer edge 57 is slightly longer than the outermost corrugation 65. The ends 67 of the corrugations adjacent the inner edge are aligned parallel to the section weld edge 29 and in spaced relationship therefrom so that a good fit and weld is achieved between the corner section 25 and the straight section 27. The point 0 is determined by the intersection of the aligned ends 67 of the corrugations which make a 90 angle with each other.

The leg 35 in which the corrugations are formed defines a plane along which the corrugations run forming crests and troughs therein. The corrugations are formed explosively by placing a sheet of metal cut into the peripheral configuration of section 25 (i.e., inner and outer edges 43 and 57 and ends 29) over a die formed substantially into the same shape as the final corrugated product of FIG. 5. The general method of manufacture is detailed in US. patent applications, Ser. No. 532,647, entitled, Explosive Formation, filed Mar. 8, 1966, and Ser. No. 447,709, entitled, Corrugation Forming by Explosives, filed Apr. 13, 1965.

After the corrugations are formed into the legs 35 of section 25, the outer edge (5759) is welded to the intermediate portion 37, which has no corrugations, to form welds 3 9 (FIG. 4) and the inner edge 43 is welded to flange pieces 23 at 41. There is no bending of the corrugations once the explosive forming operation is accomplished to fabricate the finished joint; the corner section is simply welded together at 39 and 41 instead of being bent from a single piece as the straight sections 27 of the expansion joint 27 (FIG. 3). The corrugations 49 are thereby not impaired.

The corrugations run circumferentially about the corner section providing increased rigidity in a sidewise direction along the axis of the corrugations and increased flexibility in a transverse or radial direction. This provides optimum operation of the joint with improved resiliency, and minimum stress and wear.

In operation, as the ducts 19 and 20 expand, for example, the legs 35 of the joint are forced together, shown by the dashed line 71 of FIG. 2 (and FIGS. 3 and 8). (The representation of FIG. 2 is merely intended to be descriptive as in actuality the ducts 17 and 19 may not grow in width as shown, being fixed to supports.) Similarly, the legs of the corner sections of the joint move toward one another. However, as may be seen from FIG. 6 showing an isometric view of a corner section 25 and two adjoining straight sections (27a and 27b), as the straight sections (270 and 2712) are longitudinally compressed (dashed line 71) the transverse or overall width of the joint (in the radial direction) is shortened by a distance d along both straight sections 27a and 27b. As a consequence, representative point C in the corner section tends to move laterally a distance (I in the two perpendicular directions indicated by the arrows FM) having a resultant radial and transverse force indicated by the dashed arrow T. The flexure of the two sides of the joint meeting at the corner results in a lateral movement which is restrained by the corner. This force, T, restrained by the corner by opposing radial and transverse forces (not shown) caused by the restraining effect of the duct walls, sets up compressive tensile forces in the corner tending to break, or warp the joint at the corner or inhibit the duct expansion. However, the corrugations 49 are available for compression in an accordion-like manner in the radial and transverse direction along force T relieving any tendency for the stresses to build up.

Other points C along the corner also flex along the radial lines from point 0, the flexing of the corrugations automatically compensating in the proper amount the radial vector component through which the side forces Ftd) tend to move the various corner points C. All forces PM) on the corner point C can be resolved into two components in the leg plane 35. One a radial tension force T (along the radial line from point 0) which can be readily absorbed by the flexing of the corrugations. The other component can be resolved into a circumferential or sidewise force F (i.e., tangent to the corrugation arcs); however, in this direction the corrugations provide a rigid acting leg. As a result the entire corner section including the adjoining straight sections 27a and 27b move together, rigidly, the legs acting as a plane, insuring the integrity of the welds 2,9 and uniformity of longitudinal contraction for the opposed legs around the entire joint.

The flexing of the corrugations in the radial and transverse direction together With the circumferential or sidewise rigidity provides an expansion joint capable of idealized behavior. The joint uniformly reacts about the entire circumference as a unitary joint, although constructed in readily assembled sections, without any undue stresses or restraining of the thermal movements of the ducts. No provision is made for flexing due to the compresive circumferential forces F, yet a unique and unexpected corner design condition is achieved minimizing operating stresses.

The corrugations 49 are calibrated to yield the same expansion movements as the straight portions of the joint. FIG. 7 (and the dot and dashed lines of FIG. 3) show the opposed legs 31 of the joint in expansion. Here also, the corrugations 49 contract to absorb the tendency of the corner points (FIG. 6) to radially compress the corner of the joint, precluding the building up of undesirable tensile stresses.

It should now be evident that the expansion joint of the invention is especially useful in applications where prior joints were unreliable. In addition to their utilization for uniform longitudinal expansion and contraction of the ducts, the expansion joint may be used for toggling (FIG. 9) where one side of the joint is compressed more than the other, without causing severe or uneven stress distributions about the joint. As well as the ability to calibrate the corner corrugations of the joint to maintain uniform stresses about the entire joint, the corner corrugations flex automatically so much as desired at those sections of the joint requiring additional contraction to provide uniform stresses over the entire joint.

The use of a single fold expansion joint permits the inversion of the fold into horizontal or vertical flues or ducts (FIG. 10) so that there is no possibility for the joint fold to fill with foreign material. Should inversion result in too severe flow restriction of the gases in the ducts or too large a pressure drop, therethrough, the ducts may be widened at the ends adjacent the expansion joint as shown at 81 and 83 of FIG. 11. To prevent the annular spaces 85 (or space 86 of FIG. 12) from filling with foreign matter, a cylindrical cover member 87 comprising overlapping cylindrical portions 89 and 91 is disposed adjacent the joint 15 and annular spaces 85 (or 86) welded to the ducts 17 and 19 at 93 and 95, respectively. Cylindrical portion 91 of cover member 87 has a plurality of outwardly extending threaded studs 97,

each of which extend through an elongated vertically extending slot 98 in portion 91 of the cover member. A nut 99 is turned down upon stud 97 whereby lower portion 91 of the cover member is held against upper por tion 89 of the cover member. As the joint 15 expands or contracts the overlapping cover portions 89 and 91 move vertically relative each other still overlapping to prevent foreign matter from filling space between the cover member and the joint. Drain lines 100 are provided to remove whatever foreign matter may enter the spaces through the overlapping ends of portions 89 and 91 of the cover member.

The expansion joint can be made of Corten, or other non-corrosive materials such as Margari R or stainless steel for flues and ducts where temperatures may exceed 900 F. The joint is especially useful with large straight sections where corrugations are only a part of the entire periphery of the joint, making the joint strong and resilient, and acting as an integral planar member. In applications where size permits, the straight sections 27 may be eliminated, the four corner sections then being welded to each other forming the entire joint. The joint also may be made circular with corrugated leg portions alternating with non-corrugated leg portions around the joint. Specifically, although not limited thereto, the expansion joint is useful in large ducts carrying air and flue gases between power plant steam generators, fans, air preheaters, precipitators, duct collectors and the stack, providing for thermal movements thereof. In these applications it is not unusual to find joints of size 30 feet by 70 feet. In a typical example wherein the joint is especially useful the straight sections are about five (5) feet and four (4) feet and the corner sections three and one-half (3.5) feet along each side; the width of all the straight sections are one-third /3) feet and the widest portion of the corner section two-thirds /3) feet, the ratio of the corner width to the straight section width being 2:1 considerably lower than the same ratio for prior single fold joints. Accordingly, the entire joint is relatively small, as compared to prior joints, including the width of the legs, without sacrificing strength and joint integrity. The width of the legs are still sufficiently long to absorb the required expansion in flexure. The present invention is also especially useful for the larger size joints. In addition, the single fold joint of the invention requires relatively little protection against transverse shear stresses. However, where required for transmitting loads, shear bars (not shown) may be installed across the joint.

Although the invention has been described with respect to a rectangular duct and expansion joint, the single fold expansion joint of the invention has as its principal application any shape polygon configuration (conforming to similar shape ducts which it connects) having rounded legs corners 25 with corrugations thereon adjacent the corners extending lengthwise of the peripheral boundary and straight sections 27 between the corners without corrugations, one such polygon joint being shown for example in FIG. 11A.

Although the invention has been described with respect to specific embodiments, other variations within the spirit and scope of the invention as defined in the following claims will be apparent to those skilled in the art.

What is claimed is:

1. A metallic expansion joint for connecting two passageways comprising,

two identical fiat legs having a periphery, each leg formed with an opening defining an inner peripheral edge, the legs axially disposed in spaced parallel relationship, the periphery and the inner peripheral edge defining a boundary,

an intermediate open-ended conduit portion connected to and between the legs defining with the legs a substantially U-shaped fold,

means for connecting each leg axially to one of the passageways,

each leg formed into a plurality of corrugated portions alternating with non-corrugated portions around the leg, each corrugated portion on each leg having a corresponding corrugated portion on the other leg opposite and adjacent thereto in spaced relationship, each corrugated portion comprising at least one corrugation extending substantially lengthwise of the boundary of the leg adjacent thereto.

2. A metallic expansion joint for connecting two passageways according to claim 1 wherein each corrugated portion comprises a series of spaced and substantially parallel corrugations extending substantially lengthwise of the boundary of the leg adjacent thereto.

3. A metallic expansion joint for connecting two passageways according to claim 2 wherein the periphery of the legs is substantially rectangular having rounded corners, the corrugated portions being on the legs adjacent the corners, said corrugations symmetrically arranged relative the rounded corners.

4. A metallic expansion joint for connecting two passageways according to claim 2 wherein said corrugations of each series are substantially parallel to the inner peripheral edge of the leg adjacent thereto.

5. A metallic expansion joint for connecting two passageways according to claim 4 wherein said corrugations of each series define symmetrically disposed and substantially concentric arcs and extend on the legs from adjacent the inner peripheral edge of the legs to adjacent the periphery of the legs, the inner peripheral edge adjacent the corrugations being rounded and concentric to the corrugations adjacent thereto.

6. A metallic expansion joint for connecting two passageways according to claim 2 wherein the intermediate conduit portion is connected to and between the legs adjacent the inner peripheral edge of the legs, said passageways connected to the legs at the periphery of the legs.

'7. A metallic expansion joint for connecting two passageways according to claim 5 wherein the periphery of the legs is substantially rectangular having rounded corners, the corrugated portions being on the legs adjacent the corners, said corrugations symmetrically arranged relative the rounded corners.

8. A metallic expansion joint for connecting two rectangular passageways according to claim 7 wherein said intermediate conduit portion is connected to and between the legs at the periphery of the legs, said passageways connected to the legs adjacent the inner peripheral edge of the legs.

9'. A metallic expansion joint for connecting two rectangular passageways according to claim 8 wherein the told is a squared U-shaped told.

10. A metallic expansion joint for connecting two rectangular passageways according to claim 9 wherein said expansion joint is formed from and comprises four corner joint sections including said rounded corners and four straight joint sections welded together in alternating joint section relationship, each corner and straight joint section including two leg sections and a conduit portion section therebetween formed into said squared U-shaped fold, said corrugations being on the legs of the corner sections.

11. A metallic expansion joint for connecting two rectangular passageways according to claim 10 wherein the corrugations on each leg of the corner sections are closely and uniformly spaced.

12. A metallic expansion joint for connecting two rectangular passageways according to claim 11 wherein the corrugated portions form a series of substantially sinusoidal crests and troughs.

13. A metallic expansion joint for connecting two rectangular passageways according to claim 12 wherein the corrugations adjacent the periphcry subtend a smaller angle than the corrugzuions adjacent the inner peripheral edge, the rounded corners adjacent the corrugations having a smaller radius than the radius of the rounded inner peripheral edge adjacent said corrugations and subtending a 96 angle.

14. A metallic expansion joint for connecting two rectangular passageways according to claim 13 wherein said corresponding corrugated portions are in plane symmetry. 15. A metallic expansion joint assembly for connecting two rectangular passageways comprisin",

two identical hat and substantially rectangular legs having rounded corners defining a rounded corner rectangular outer peripheral edge, each leg having an opening defining an inner peripheral edge, the legs axially disposed in spaced parallel relationship, each of said legs formed from and comprising four corner sections and four straight rectangular sections each having section ends welded together in alterhating section relationship, each section of each leg having a corresponding section in the other leg disposed opposite thereto in spaced parallel relationship, the corner sections and the rectangular sections including inner and outer edges between the section ends, the inner edges of the sections aligned forming the inner peripheral edge of the leg and the outer edges of the sections aligned forming the outer peripheral edge of the leg, said inner and outer edges of the corner sections being rounded, the perpendicular distance between inner and outer edges of all the straight rectangular sections being the same; an intermediate open-ended conduit portion having a uniform rounded corner rectangular cross-sectional opening identical to the outer peripheral edge of the legs, the conduit portion connected to and between the outer peripheral edge of the legs at the conduit ends defining a square Ushaped fold, the conduit portion being formed from and comprising four curved-rectangular corner portions and four rectangle portions corresponding to the four corner and four straight sections of the legs, each corner and rectangle portion having side edges and leg edges and welded together in alternating corner and rectangle portion relationship along the side edges, the leg edges of the alternating portions being aligned to define the conduit ends, said leg edges of the curved-rectangular corner portions being rounded conforming to the rounded corners of the outer edges of corresponding corner sections and welded thereto and therebetweeu forming the square U-shaped fold at the corner sections, said leg edges of the rectangle portion of the conduit portion forming with the corresponding straight rectangular sections of the legs an unwelded single metallic piece bent into the square U-shaped fold thereat; flanged means for connecting each leg axially to one of the passageways, the legs connected to the passageways adjacent the inner peripheral edge of the legs;

each corner section of the leg formed into a plurality of corrugations defining a series of concentric arcs with one another and with the inner edge of the corner section, the inner edge of the corner section forming an inner circular arc edgs of approximately the outer edge of the corner section forming an outer circular arc edge of 90 having a radius smaller than the radius of the inner arc edge and two equal length tangent edges extending from and tangent to the ends of the outer circular arc edge, said tangent edges aligned with the outer edges of the straight rectangular sections of the legs, the corrugations and inner and outer circular arc edges being symmetrically disposed;

the corrugations formed in each corner section extending in uniform spaced relationship concentrically from adjacent the inner edge of the corner section to adjacent the outer edge of the corner section, the corrugations adjacent the inner edge defining concentric circular arcs of 90 having aligned ends, the

ends of said corrugations adjacent the inner edge aligned parallel to and in spaced relationship to the welded section ends;

the corrugations between said corrugations adjacent the inner edge and the outer circular arc edge decreasingly in length and angle subtended approaching the outer edge;

the corrugations in corresponding corner sections being in plane symmetry defining a varying spaced region between the legs at the corner sections.

16. A- metallic expansion joint assembly for connecting two rectangular passageways according to claim 15 wherein the corrugations form a series of substantially sinusoidal crests and troughs.

References Cited UNITED STATES PATENTS 2,797,112 6/1957 Ziebold 285286 X 3,099,467 7/1963 Godshalk 285229 X 3,254,910 6/1966 PoOle et a1. 285226 10 EDWARD C. ALLEN, Primary Examiner.

THOMAS F. CALLAGHAN, Examiner. 

1. A METALLIC EXPANSION JOINT FOR CONNECTING TWO PASSAGEWAYS COMPRISING, TWO IDENTICAL FLAT LEGS HAVING A PERIPHERY, EACH LEG FORMED WITH AN OPENING DEFINING AN INNER PERIPHERAL EDGE, THE LEGS AXIALLY DISPOSED IN SPACED PARALLEL RELATIONSHIP, THE PERIPHERY AND THE INNER PERIPHERAL EDGE DEFINING A BOUNDARY, AN INTERMEDIATE OPEN-ENDED CONDUIT PORTION CONNECTED TO AND BETWEEN THE LEGS DEFINING WITH THE LEGS A SUBSTANTIALLY U-SHAPED FOLD, MEANS FOR CONNECTING EACH LEG AXIALLY TO ONE OF THE PASSAGEWAYS, 